I don't see any reason to presume that the entire Anglosphere is that ignorant about Vietnamese culture. Douglas Lilburn found a Vietnamese song recording to use in his electronic piece "Poem in Time of War" around 1970. I had Vietnamese friends in Auckland a bit before that. New Zealand Communists like Rewi Alley visited Vietnam during the war and reported back. I have CDs of Vietnamese classical music and a Vietnamese flutemaker is a Facebook friend. I know somebody with a Vietnamese partner in a three-months-in-the-year relationship. A Vietnamese novel about the war was a UK best seller. It's not like it's totally isolated from the West or ever was.

In terms of political effectiveness, the distractions of American middlebrow culture did far more to keep the war going than any oppositional songs did to stop it. Phil Ochs was politically insignificant compared to Frank Sinatra.